1. Field of the Invention
The present invention relates to modules including high-frequency switches, and specifically to a high-frequency switch module including a high-frequency switch including a common input/output terminal and a substrate on which the switch is mounted.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2008-271420 discloses a high-frequency switch module for cellular phones.
FIG. 1 is a perspective view of a high-frequency switch module disclosed in Japanese Unexamined Patent Application Publication No. 2008-271420. In this high-frequency switch module 1, SAW filters 50, 55, and 60, capacitors C1, C2, and C3, and an inductor L1, together with an FET switch circuit, are mounted on a multilayer substrate 5. The FET switch circuit includes transmission signal terminals, reception signal terminals, and an antenna terminal. In addition, control signal terminals for selectively connecting the antenna terminal to a specified signal terminal are provided. It is stated in Japanese Unexamined Patent Application Publication No. 2008-271420 that in order to prevent deterioration of insertion loss characteristics in a pass band caused by leakage of part of a transmission signal or received signal to control terminals through control signal lines connected to the control signal terminals, a control circuit is isolated using a ground electrode, thereby improving isolation between the control signal lines and transmitter/receiver circuits.
In Japanese Unexamined Patent Application Publication No. 2008-271420, a plurality of ground electrodes are provided in the multilayer substrate and are connected to one another using via holes. The FET switch requires not only transmission/reception signal lines and corresponding ground lines, but also ground lines used to apply control signals for switching the switch.
When the control signal lines are arranged between a plurality of ground electrodes as described in Japanese Unexamined Patent Application Publication No. 2008-271420, direct interference between the control signal lines and the transmission/reception lines is reduced. However, when the ground electrode for the transmission/reception signals and the ground electrode for the control signal lines are the same electrode, a high-power signal leaks from the transmission terminals or the like to a logic circuit unit through the common ground electrode, resulting in a problem in that high-frequency characteristics such as the harmonic wave distortion characteristics of the switch are deteriorated because the logic circuit cannot operate normally.